Optical sensors for combustion control

ABSTRACT

Certain embodiments of the invention may include systems and methods for providing optical sensors for combustion control. According to an example embodiment of the invention, a method for controlling combustion parameters associated with a gas turbine combustor is provided. The method can include providing at least one optical path adjacent to a flame region in the combustor, detecting at least a portion of the light emission from the flame region within the at least one optical path, and controlling at least one of the combustion parameters based in part on the detected light emission.

FIELD OF THE INVENTION

This invention generally relates to sensors, and more particularlyrelates to optical sensors for combustion control.

BACKGROUND OF THE INVENTION

Modern industrial gas turbines are required to convert energy at a highefficiency while producing minimum polluting emissions. But these tworequirements are at odds with each other since higher efficiencies aregenerally achieved by increasing overall gas temperature in thecombustion chambers, while pollutants such as nitrogen oxide aretypically reduced by lowering the maximum gas temperature. The maximumgas temperature can be reduced by maintaining a lean fuel-to-air ratioin the combustion chamber, but if the fuel/air mixture is too lean,incomplete fuel combustion can produce excessive carbon monoxide andunburned hydrocarbons. Therefore, the temperature in the reaction zonemust be adequate to support complete combustion.

To balance the conflicting needs for increased efficiency and reducedemissions, extremely precise control is required to adjust the fuel/airmixture in the reaction zones of the combustors. Systems have beenproposed for controlling the fuel/air mixture by monitoring variouscombustion parameters, and using the measured parameters as input tocontrol the fuel system. For example, one conventional system includes acontrol system where fuel flow rates, pressure levels, and dischargeexhaust temperature distributions are utilized as input for setting fueltrim control valves.

Other techniques for controlling combustion dynamics include measuringlight emission from the combustion burner flame, and using the measuredsignal to control certain combustion parameters. For example, oneconventional system uses a closed loop feedback system employing asilicon carbide photodiode to sense the combustion flame temperature viathe measurement of ultraviolet radiation intensity. The sensedultraviolet radiation is utilized to control the fuel/air ratio of thefuel mixture to keep the temperature of the flame below a predeterminedlevel associated with a desired low level of nitrogen oxides.

Other conventional systems can use optical fibers for gathering andtransmitting light from a combustion region to detectors. Yet otherconventional systems can use a video camera to capture images of theflame primarily for monitoring the presence or absence of a flame.

A need remains for improved systems and methods for providing opticalsensors.

BRIEF SUMMARY OF THE INVENTION

Some or all of the above needs may be addressed by certain embodimentsof the invention. Certain embodiments of the invention may includesystems and methods for providing optical sensors for combustioncontrol.

According to an example embodiment of the invention, a method forcontrolling combustion parameters associated with a gas turbinecombustor is provided. The method can include providing at least oneoptical path adjacent to a flame region in the combustor, detecting atleast a portion of the light emission from the flame region within theat least one optical path, and controlling at least one of thecombustion parameters based in part on the detected light emission.

According to another example embodiment, a system for controllingcombustion parameters associated with a gas turbine combustor isprovided. The system can include at least one optical port adjacent to aflame region in the combustor, one or more photodetectors incommunication with the at least one optical port operable to detect atleast a portion of light emission from the flame region, and at leastone control device operable to control one or more combustion parametersbased at least in part on one or more signals from the one or more photodetectors.

According to another example embodiment, a gas turbine is provided. Thegas turbine can include a combustor, at least one optical port adjacentto a flame region in the combustor, one or more photodetectors incommunication with the at least one optical port, and operable to detectat least a portion of light emission from the flame region, and at leastone control device operable to control one or more combustion parametersbased at least in part on one or more signals from the one or morephotodetectors.

Other embodiments and aspects of the invention are described in detailherein and are considered a part of the claimed invention. Otherembodiments and aspects can be understood with reference to thedescription and to the drawings.

BRIEF DESCRIPTION OF THE FIGURES

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 depicts an illustrative optical sensor in communication with theflame region of a turbine combustor, according to an example embodimentof the invention.

FIG. 2 illustrates the optical sensor imaging system, in accordance witha narrow field-of-view example embodiment of the invention, where thelens is positioned to collect light primarily from one flame region ofthe combustor.

FIG. 3 illustrates the optical sensor imaging system, in accordance witha wide field-of-view example embodiment of the invention, where the lensis positioned to collect light from multiple flame regions of thecombustor.

FIG. 4 is an example method flowchart for measuring flame combustionparameters, according to an example embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described more fully hereinafterwith reference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

An embodiment of the invention may enable combustion parameters to bemeasured in a turbine combustor by selectively detecting spatial,temporal, and/or spectral light emissions from combustor burner flames.According to embodiments of the invention, the measured combustionparameters may in turn be utilized to control various parameters of thecombustor, including, but not limited to fuel flow rates, fuel/airratios, and fuel flow distributions to optimize nitrous oxide emissions,dynamic pressure oscillations, and fuel efficiencies.

According to example embodiments of the invention, chemiluminescenceemissions from one or more flames in a combustor may be monitored usingoptical detectors. The light energy emissions may be spectrally filteredto identify the partial contribution of the total light emission fromspecific excited-state species such as OH*, CH*, C2* and CO2*. Ratios ofthese measured signals may be correlated to the fuel-to-air ratio, heatrelease rate, and temperature. According to example embodiments, thetime-resolved output from optical detectors may be analyzed to revealunsteady phenomena associated with the combustion, and may be used toindicate combustion-acoustic oscillations (combustion dynamics),incipient flame blowout, and flame extinction. In addition, the outputsignals may be used as feedback for use in a closed-loop combustioncontrol system. Various sensor options and configurations for combustioncontrol applications, according to embodiments of the invention, willnow be described with reference to the accompanying figures.

FIG. 1 illustrates an example can combustor with a flame sensor andcontrol system 100 for controlling combustion parameters associated witha gas turbine combustor, according to an example embodiment of theinvention. The flame sensor components may be placed or mounted adjacentto the can combustor 102 and may selectively detect light emission fromthe flames 104 within the can combustor 102 near the flame region 106 ofthe can combustor 102. The light emission from at least a portion of theburner flames 104 may pass through an optical port 112 in the side wallof the can combustor 102 and may be focused, imaged, or transformed byone or more lenses 114. According to example embodiments of theinvention, the one or more lenses 114 may be moveable in order to varythe optical system field of view, as will be discussed in reference toFIGS. 2 and 3 below.

According to an example embodiment of the invention, and with continuedreference to FIG. 1, an aperture 130 may be placed adjacent to the lens114 in order to control the intensity of the light from the flames 104.The aperture 130 may also be utilized for adjusting the optical systemdepth of field. According to an example embodiment of the invention, aportion of the spectrum of the light from the burner flames 104 may befiltered before reaching the first optical detector 122 by a firstoptical filter 118 to aid in identifying the partial contribution of thetotal light emission from specific excited-state species that produceoptical radiation in narrow-band portions of the optical spectrum.According to example embodiments of the invention, the optical detector122 may be selected for its response within wavelength spectra windowsof interest. For example, a silicon carbide (SiC) photo detector may beselected because of its sensitivity to the ultra violet portion of thewavelength spectrum, and therefore, may be suitable for sensing theemission from the excited state OH* radical in the 300 nm wavelengthrange. The OH* emission can be a primary indicator of chemical reactionintensity (heat release) and therefore, wavelengths in the 300 nm regionmay be used to determine gas temperature. According to anotherembodiment, a silicon (Si) photo detector may be utilized for monitoringthe emission from chemical species in the 400 to 1000 nm spectrumincluding CH* (about 430 nm) and C2* (about 514 nm). These flameradicals have been found to be proportional to heat release and localfuel-to-air ratio in pre-mixed flames.

According to an example embodiment of the invention, a beam splitter 116may be utilized to redirect a portion of the light emission through asecond optical filter 120 to a second optical detector 124. The spectraltransmission characteristics of the first optical filter 118 and thesecond optical filter 120 may be selected such that specificexcited-state species ratios may be measured with increased accuracywhile partially eliminating interfering background emissions fromexcited-state species that may be of less interest. According to anexample embodiment, the first optical filter 118 and the second opticalfilter 120 may be interchangeable, fixed, or tunable. According to anexample embodiment, the optical filters 118 120 may be narrowbandfilters. Fabry-Perot or dichroic optical filters are examples of thetypes of filters that may be utilized for transmitting certainwavelength bands while attenuating or reflecting out-of-bandwavelengths.

Also shown in FIG. 1 are blocks representing the detector electronics126 and the combustion control system 128. According to an exampleembodiment, the detector electronics 126 may be operable to condition,amplify, filter, and process the signals from the optical detectors 122,124. The detector electronics 126 may also provide control for adjustingthe diameter of the aperture 130 and/or for positioning the lens 114.The output signal from the detector electronics may be used as a controlsignal for the combustion control system 128. For example, according toan embodiment of the invention, the measured ratio of CH to OHchemiluminescence (CH*/OH*) may be utilized as feedback in thecombustion control system 128, and may provide a control to dynamicallyadjust the fuel/air ratio.

FIG. 2 depicts an end view of combustion zone and a narrow field-of-viewflame imaging and sensor system 200, according to an example embodimentof the invention. For clarity, the beam splitter 116, second opticaldetector 124, and the first and second optical filters 118, 120 areomitted from this figure. According to an example embodiment, a portionof the light emission from the burner flames 104 may be imaged onto thesurface of the optical detector 122. In an example embodiment, the flameobject 208 may be imaged at the image plane 204 to produce a flame image210. In an example embodiment, the optical detector 122 at the imageplane 204 may comprise a single sensing element having a finite sensingarea, and therefore, the optical radiation that is imaged onto thesensor area may produce an output signal proportional to the integratedsum of the total optical energy incident on the detector. According tooptical imaging theory for thin lenses, the field of view may bedetermined by a combination of factors including the placement of thelens 114, the width of the optical detector 122, the focal length f 202of the lens 114, the object distance 212, and the image distance 214.The approximate relationship between the object distance d_(o) 212, theimage distance d_(i) 214, and the focal length f of the lens may beexpressed as 1/d_(o) +1/d _(i)=1/f. The image magnification can beexpressed as M=−d_(i)/d_(o), where the minus sign indicates that theimage is reversed with respect to the optical axis 216.

FIG. 2 shows an example narrow field-of-view embodiment where a lens114, having a focal length f 202, is placed in an example first positionat an image distance 214 from the image plane 204, where the image plane204 is coincident with the surface of the optical detector 122. In thisexample configuration, the flame object 208 located at the object plane206 produces a flame image 210 at the image plane 204. The exampleconfiguration shown will also allow a small portion of the light fromthe non-imaged burner flames 104 to be incident on the optical detector122, but the majority of the output signal produced by the detector willbe related to the portion of the imaged flame 210 that falls on theactive area of the detector. In an example embodiment of the invention,the detector may be adjustable such that it is able to move along theimage plane to enable different burner flame 104 regions to be selectedfor detecting.

According to an example embodiment of the invention, a fixed oradjustable aperture (not shown) may be placed adjacent to the detectorto limit unwanted portions of the flame image 210 that may otherwise beincident on the optical detector 122. The fixed or adjustable aperturemay move parallel to the image plane 204 to selectively transmit regionsof the burner flame image 210 for sensing with the detector, thereby,providing an alternative to moving the detector to enable differentburner flame 104 regions to be selected for detecting. According to anexample embodiment of the invention, multiple detectors may be utilizedin the image plane 204 to simultaneously detect or monitor spatiallyseparated regions of the burner flames 104.

FIG. 3 depicts an end view of combustion zone wide field-of-view flameimaging and sensor system 300, according to an example embodiment of theinvention. The beam splitter 116, second optical detector 124, and thefirst and second optical filters 118, 120 are omitted from this figurefor clarity. In this example depiction, the movable lens 114 ispositioned closer to the optical detector 122 and image plane 204 ascompared to the depiction shown in FIG. 2. One consequence of moving thelens 114 closer to the optical detector 122 is that the distance betweenthe image plane 204 and the object plane 206 may increase approximatelyaccording to the thin lens formula 1/d_(o)+1/d_(i) =1/f. Anotherconsequence of moving the lens 114 closer to the optical detector 122 isthat size of the flame image 210 may decrease approximately according tothe magnification M=−d_(i)/d_(o). Therefore, depending on the geometryof the imaging system, the position of the lens 114, and the area of theoptical detector 122, the flame image 210 incident on the opticaldetector 122 may comprise the image of multiple burner flame objects208. Thus, by adjusting the position of the moveable lens 114 towardsthe detector, the imaging system may selectively collect and image lightemission from multiple combustor flames 104 (i.e., thewide-field-of-view embodiment as shown in FIG. 3). Conversely, byadjusting the position of the moveable lens 114 away from the detector,the imaging system may selectively collect and image light emissionprimarily from a single combustor flame 104 (i.e., thenarrow-field-of-view embodiment as shown in FIG. 2).

According to example embodiments, the optical detectors 122, 124 may beselected to measure one- or two-dimensional representations of theprimary combustion parameters. For example, optical detectors 122, 124may comprise an array, rather than a single sensitive element.Therefore, the arrays may capture flame images over a two-dimensionalgrid, similar to a digital camera system. Examples of such arrays caninclude, but are not limited to, charged coupled devices (CCD),complementary metal-oxide semiconductor (CMOS) arrays, and indiumgallium arsenide (InGaAs) arrays.

An example method for measuring flame parameters for use in controllingcombustion characteristics will now be described with reference to theflowchart 400 of FIG. 4. Beginning in block 402 and according to anexample embodiment of the invention, at least one optical port such as112 may be provided in the body of the turbine can combustor such as 102adjacent to the flame region such as 106. The optical port may beconstructed from high temperature resistant, optically transparentmaterial such as quartz, sapphire, or other suitable materials with lowloss and a transmission bandwidth appropriate for the wavelengths ofinterest. Light emissions from the burner flames such as 104 may betransmitted through the optical port 112 to the remaining opticalsystem, which may reside outside of the can combustor 102 where thermalisolation, cooling, etc., can be used to protect the optics, detectors,and associated electronics and hardware.

In block 404, according to an example embodiment of the invention, theoptical system may comprise a variable aperture such as 130 adjacent tothe optical port such as 112. The variable aperture 130 may be manuallyadjusted, or it may be motorized so that the diameter of the apertureopening may be electronically controlled to adjust the total influx oflight reaching the optical detectors such as 122, 124. The variableaperture 130 may also be used to provide a depth-of-field control forthe optical imaging system. According to one example embodiment, thevariable aperture 130 may be mounted adjacent to the optical port 112.The optical imaging system may additionally comprise an adjustable ormoveable lens such as 114 or lens system adjacent to the variableaperture 130, at least one optical detector 122 responsive to at leastthe portion of the burner flame such as 104 emission spectrum ofinterest, and at least one optical filter such as 118 in the opticalpath before the optical detector 122 and operable to selectivelytransmit a portion of the burner flame 104 emission spectrum to theoptical detector 122.

Decision block 406 depicts two settings available for the opticalimaging system: wide and narrow field-of-view. According to an exampleembodiment, the binary (wide or narrow) settings may be accomplished byselectively inserting or removing fixed lenses into the appropriateposition along the optical path. However, according to another exampleembodiment, the lens such as 114 may be moveable, and therefore, thefield-of-view may also be variable, and may be set as desired at anyintermediate setting between the extreme wide and narrow field-of-viewsettings.

In block 408, the optical imaging system may be set to comprise a widefield-of-view, for example, by adjusting the distance between the lenssuch as 114 and the optical detector such as 122 to be approximately thefocal length f 202 of the lens 114 (as depicted in FIG. 3).

In block 410, the optical imaging system may be set to comprise a narrowfield-of-view, for example, by adjusting the distance between the lens114 and the optical detector 122 to be approximately twice the focallength f 202 of the lens 114 (as depicted in FIG. 2). Physicalconstraints may limit the actual movement of the lens 114, therefore, itis to be understood that the invention is not to be limited to thespecific embodiments disclosed, and that additional lens methods can beutilized in accordance with embodiments of the invention.

Block 412 indicates that an optional ratiometric technique may beutilized for simultaneously measuring and relating two or morewavelengths of interest. According to an example embodiment, theratiometric measurement technique may be achieved by providing a beamsplitter 116, a first optical filter 118, a first optical detector 122,a second optical filter 120, and a second optical detector 124, as shownin FIG. 1. In one example embodiment, the ratiometric measurement may beachieved by utilizing the first optical filter 118 and the first opticaldetector 122 to selectively measure the emission response from oneexcited species (for example CH* near 425 nm) and simultaneouslymeasuring the response of another excited species (for example, OH* near310 nm) using the second optical filter 120 and second optical detector124. The ratiometric measurement may be achieved, for example, bydividing the response of the CH* by the response of the OH*. The ratioCH*/OH* has been shown to relate to the equivalence ratio (φ), which isa universal function related to many combustion characteristics. Oneother aspect of the ratiometric measurement technique is that backgroundradiation common to each detector may be eliminated, thereby increasingthe signal to noise ratio.

In block 414, and according to an example embodiment, the combustionflame properties may be measured. The properties may comprise theemission spectra, time perturbations, flame images, or a combination ofthese properties. A measurement may include both spectral and timevarying information. For example, portions of the flame emission spectramay be selected by filtering, and the filtered emission may be incidentupon one or more optical detectors 122, 124 to produce a time varyingsignal that can be utilized in block 416 to extract combustionparameters from the measurements. The extracted combustion parametersmay be used in block 418 to control and optimize the combustioncharacteristics using other methods in accordance with embodiments ofthe invention. For example, the extracted combustion parameters may beutilized in a feedback control loop for adjusting the fuel flow,fuel-to-air ratio, fuel distribution among the burners, etc.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A method for controlling combustion parameters associated with a gasturbine combustor, the method comprising: providing at least one opticalpath adjacent to a flame region in the combustor; detecting within theat least one optical path at least a portion of light emission from theflame region; and controlling at least one of the combustion parametersbased in part on the detected light emission.
 2. The method of claim 1,wherein detecting within the at least one optical path at least aportion of light emission from the flame region comprises selectivelyfiltering the light emission to isolate spectral information associatedwith the light emission.
 3. The method of claim 1, wherein providing atleast one optical path adjacent to a flame region in the combustorcomprises providing a lens operable to image at least a portion of thelight emission from the flame region.
 4. The method of claim 3, whereinproviding at least one optical path adjacent to a flame region in thecombustor comprises providing a moveable lens operable to variablyadjust at least a field of view associated with the optical path.
 5. Themethod of claim 1, wherein detecting within the at least one opticalpath at least a portion of light emission from the flame regioncomprises filtering least a portion of the light with a first filter anddetecting at least a portion of the first filtered light with at leastone first photodetector.
 6. The method of claim 5, wherein detectingwithin the at least one optical path at least a portion of lightemission from the flame region comprises filtering least a portion ofthe light with a second filter and detecting at least a portion of thesecond filtered light with at least one second photodetector, whereinthe second filter differs from the first filter.
 7. The method of claim6, wherein controlling at least one of the combustion parameters isbased in part on signals from the at least one first photodetector andthe at least one second photodetector.
 8. The method of claim 1, whereincontrolling at least one of the combustion parameters based in part onthe detected light emission comprises controlling at least one of fuelflow rate, fuel flow distribution, air/fuel ratio, combustion flameoscillations, combustion flame extinction, heat release ratio, or flametemperature.
 9. The method of claim 1, wherein providing at least oneoptical path adjacent to a flame region in the combustor comprisesproviding a beam splitter to spatially separate optical paths.
 10. Asystem for controlling combustion parameters associated with a gasturbine combustor, the system comprising: at least one optical portadjacent to a flame region in the combustor; one or more photodetectorsin communication with the at least one optical port operable to detectat least a portion of light emission from the flame region; and at leastone control device operable to control one or more combustion parametersbased at least in part on one or more signals from the one or morephotodetectors.
 11. The system of claim 10, further comprising: one ormore optical filters operable to isolate spectral information associatedwith the light emission.
 12. The system of claim 10, further comprising:at least one lens operable to image at least a portion of light emissionfrom the flame region.
 13. The system of claim 12, wherein the at leastone lens comprises moveable lens operable to variably adjust at least afield of view associated with the optical path.
 14. The system of claim10, further comprising: at least one first optical filter, wherein theat least one first optical filter is in communication with at least onefirst photodetector.
 15. The system of claim 14, further comprising: atleast one second optical filter, wherein the at least one second opticalfilter is in communication with at least one second photodetector. 16.The system of claim 15, wherein the at least one control device isoperable to control the one or more combustion parameters based at leastin part on signals from the at least one first photodetector and the atleast one second photodetector.
 17. The system of claim 10, wherein theat least one control device operable to control one or more combustionparameters is operable to control at least one of fuel flow rate, fuelflow distribution, air/fuel ratio, combustion flame oscillations,combustion flame extinction, heat release ratio, or flame temperature.18. The system of claim 10, further comprising: at least one beamsplitter operable to spatially separate light emission from the flameregion.
 19. The system of claim 10, wherein the one or morephotodetectors are responsive to at least a portion of the ultravioletspectrum.
 20. A gas turbine comprising: a combustor; at least oneoptical port adjacent to a flame region in the combustor; one or morephotodetectors in communication with the at least one optical port, andoperable to detect at least a portion of light emission from the flameregion; and at least one control device operable to control one or morecombustion parameters based at least in part on one or more signals fromthe one or more photodetectors.